The invention relates to a measuring method of a strictured butt-jointed seam in laser welding, and a device; two-dimension and three-dimension visual information is combined together organically, the information of three-dimension position, normal vector and weld width of a seam center is obtained at a same measurement position by carrying out calibration to a CCD camera and two laser planes and utilizing a seam image containing three laser stripes. The device comprises a telecentric lens, the CCD camera, an image grabbing card, a band-pass filter and a computer. Each linear light source laser projects three converged laser planes, the laser stripes formed by the intersection of all the laser planes and the plane which is vertical to the principal optic axis of the CCD camera are approximately parallel. The first and third linear light source lasers are symmetrically installed on the left and the right sides of the CCD camera and form the angles of 15 degrees to 60 degrees with the principal optic axis of the CCD camera; the second linear light source laser is symmetrically installed at the front side or the back side of the CCD camera and forms the angles of 10 degrees to 30 degrees with the principal optic axis of the CCD camera. The device has simple structure, with rich measurement information.